of course before doing that, ask yourself this question: why do you want to get married? if you have a very solid reason, then go ahead, if not, try again

if I were you, I will subtly drop hints to let her know that we want to commit ourself for the rest of the life. if subtle hints don't work, try obvious hint. of course there are a lot of ways of hinting, it can be in a jovial manner if you don't want to pressure her too much until she distance herself from this

and also it's not about how long you know her, it's how well you know her, a lot of times we might think that we know our significant others for a long time and we know them well enough but that's not always the case, there are a lot of communications and understanding involved